Pyrrolidones are useful organic solvents and chemical intermediates. N-methyl-2-pyrrolidone, for example, is widely used in cleaners and coating removers, and is a less toxic alternative to halogenated hydrocarbons such as methylene chloride. In one commercial process, N-methyl-2-pyrrolidone is produced in a multi-step process from allyl alcohol. Hydroformylation of allyl alcohol gives 4-hydroxybutanal, which is dehydrogenated to .gamma., -butyrolactone, which is then reacted with methylamine to give N-methyl-2-pyrrolidone. A potentially more attractive route converts N-methylallylamine directly to N-methyl-2-pyrrolidone in a cyclocarbonylation process: ##STR1##
Cyclocarbonylation of allylic amines to pyrrolidones using cobalt carbonyl catalysts is described by Falbe and coworkers (Tetrahedron Lett. (1965) 2677; Chem. Ber. 98 (1965) 1228; Ang. Chem. I.E. Eng. 5 (1966) 435). The reaction requires high temperatures (230.degree.-280.degree. C.) and pressures (300 atmospheres), and gives pyridine by-products under some conditions.
McCoy et al. (U.S. Pat. No. 3,714,185) teach phosphine complexes of cobalt and rhodium as catalysts for making 2-pyrrolidone from allyl amine. The phosphine catalysts permit preparation of the pyrrolidones at lower temperatures and pressures than those reported earlier.
Knifton (U.S. Pat. No. 4,111,952; J. Organometal. Chem. 188 (1980) 223) teaches to use rhodium catalysts to prepare pyrrolidones from allyl halides or allylic amines. Pressures of at least about 10 atmospheres are required for substantial conversion of the allylic amine to the pyrrolidone products.
Improved cyclocarbonylation processes are needed. An ideal process would allow short reaction times and would result in high conversions of allylic amines with good selectivity to pyrrolidones at relatively mild temperatures and low pressures. Preferably, the pyrrolidone would be the only carbonylation product.